Apparatus For Denitrifying Wastewater

ABSTRACT

Disclosed is an apparatus for denitrifying a solution that includes a denitrification tank configured to receive a portion of the solution for a period of time. Controlling an amount, duration and frequency of introduction of polyethylene glycol into the solution promotes indigenous heterotrophic bacteria depleting dissolved oxygen in the solution and obtaining oxygen from nitrate in the solution.

REFERENCE TO EARLIER APPLICATION

This Application incorporates by reference and is a continuation-in-partof U.S. patent application Ser. No. 11/721,995 filed on Jun. 18, 2007.

BACKGROUND OF THE INVENTION

Denitrification of solutions is useful for many reasons, such aslimiting the total nitrogen discharged in wastewater to comply withlocal permits. Other reasons include: improving freshwater quality;controlling alkalinity and oxygen recovery, producing stabilizedeffluent, and reducing issues stemming from sludge accumulation in theclarifier.

Removing nitrogen from wastewater requires understanding the differentforms of nitrogen and some commonly referred to terms:

Total Nitrogen (TN) is the sum of all nitrogen forms or:

Total Nitrogen=TKN+NO₂ ⁻ +NO₃ ⁻

where:

TKN stands for Total Kjeldahl Nitrogen, which is the sum of: NH₃+OrganicNitrogen;

NH3 stands for Ammonia Nitrogen or Ammonium ion (NH₄ ⁻ );

Organic Nitrogen is derived from amino acids, proteins, urea, uric acid,etc.;

NO₂ ⁻ represents a Nitrite ion;

NO₃ ⁻ represents a Nitrate ion; and

N₂ represents Nitrogen Gas.

Refractory Nitrogen cannot be decomposed biologically.

Alkalinity is defined as the ability to resist a drop in pH. For everypart ammonia (NH₃) converted to nitrate (NO₃ ⁻ ), 7.1 parts ofalkalinity are depleted, and for every part nitrate (NO₃ ⁻ ) removed,3.6 parts of alkalinity are recovered.

An anoxic zone is a basin, or portion that is mixed, but not aerated.The dissolved oxygen levels must be less than 1.0 mg/L, and avoid as lowas 0.0 mg/L. In an anoxic zone, denitrifying bacteria derive oxygen fromthe nitrate (NO₃ ⁻ ) compounds.

Nitrification and denitrification are two terms that are commonlymisunderstood. Both are individually distinct processes. Nitrificationis the conversion of ammonia (NH₃) to nitrate (NO₃ ⁻ ). This is atwo-step process involving oxygen and two types of bacteria,Nitrosomonas and Nitrobacter, known collectively as nitrifiers,represented as follows:

Ammonia(NH₃)+Oxygen(O₂)+Alkalinity+Nitrosomonas=Nitrite(NO₂ ⁻)+Oxygen(O₂)+Alkalinity+Nitrobacter=Nitrate(NO₃ ⁻ )

Nitrite (NO₂ ⁻ ) is unstable and is easily converted into nitrate. Thetotal conversion of ammonia (NH₃) to nitrate (NO₃ ⁻ ) requires 4.6 partsoxygen and 7.1 parts alkalinity to convert 1 part ammonia (NH₃).

Denitrification is the conversion of nitrate (NO₃ ⁻ ) to nitrogen gas(N₂). Heterotrophic bacteria use nitrate (NO₃ ⁻ ) as an oxygen sourceunder anoxic conditions to break down organic substances as follows:

Nitrates(NO₃ ⁻ )+Organics+Heterotrophic bacteria=NitrogenGas+Oxygen+Alkalinity

In practice, only certain forms of nitrogen are monitored in wastewatertreatment facilities with specialized testing equipment. Testing for TKNinvolves a test that many wastewater treatment facility laboratories arenot equipped to perform. If testing for TKN is not possible, othermethods are used for monitoring the nitrogen cycle.

Typically, ammonia (NH₃) values are approximately 60% of the TKN values,and the organic nitrogen generally is removed to the settled sludge.Also, total Kjeldahl nitrogen (TKN) generally equals 15-20% of theBiochemical Oxygen Demand (BOD) of the raw sewage. Testing the followingaid in monitoring and controlling the nitrogen cycle: pH, alkalinity,ammonia (NH₃), nitrite (NO₂ ⁻ ) and nitrate (NO₃ ⁻ ). All majorlaboratory supply companies sell field test kits that are inexpensive,easy to use, and provide quick relatively accurate results.

Having a good understanding of the form and extent of nitrogen in awastewater treatment facility requires a good sampling program thatgives a complete profile of the system. The first sampling point shouldtest the raw influent, or primary effluent if the system has a primaryclarifier. Typically, what enters the system is high in alkalinity andammonia (NH₃) with little to no nitrite (NO₂₋) or nitrate (NO₃ ⁻ ). Aquick way to determine if additional alkalinity may be needed is tomultiply the amount of ammonia (NH₃) by 7.1 mg/L. If this number exceedsthe influent alkalinity concentration, sodium hydroxide or lime may beneeded to be added to the aeration tank.

pH is significant because, when ammonia (NH₃) begins converting tonitrate (NO₃ ⁻ ) in the aeration tank, many hydrogen ions are released.When alkalinity drops below 50 mg/L, pH can drop dramatically. The pH ofthe aeration tank should never drop below 6.5, otherwise desiredbiological activity will be inhibited and toxic ammonia (NH₃) can bleedthrough the system to the environment.

Ammonia (NH₃) should have extremely low concentrations. Nitrite (NO₂ ⁻ )should be very low to non-detectable, with the majority of the nitrogenin the nitrate (NO₃ ⁻ ) form. If a suitable environment is maintained inthe aeration tank, most of the ammonia (NH₃) will be converted tonitrate (NO₃ ⁻ ) by the time it leaves the tank.

All tested nitrite (NO₂ ⁻ ) levels should be very low. High levels ofnitrite (NO₂ ⁻ ) in the system indicate an existing or anticipateproblem with the nitrification cycle.

Nitrosomonas bacteria are hardier than Nitrobacter bacteria. If theNitrobacter bacteria die off, the Nitrosomonas bacteria will continueworking on the ammonia (NH₃) and the cycle will overload with highlevels of nitrite (NO₂₋). An effluent with high nitrite (NO₂₋)concentrations is difficult to disinfect because of the tremendouschlorine demand it poses.

Other problems also can occur during nitrification. A decrease in theaeration tank pH due to insufficient alkalinity causes ammonia (NH₃) tobleed through the system, which causes decreased microbiologicalactivity. Other factors that prevent complete nitrification include: alack of dissolved oxygen; high mixed liquor suspended solids; low meancell retention time; and cold temperatures.

All of these factors can inhibit the nitrification cycle. High ammonia(NH₃) discharges can affect toxicity testing. High nitrite (NO₂ ⁻ )levels will cause a tremendous chlorine demand making disinfectiondifficult, jeopardizing fecal coliform limits. Leaving sludge that ishigh in nitrate (NO₃ ⁻ ) too long in a secondary clarifier can cause itto rise to the surface when the nitrogen gas is released. This is messyand jeopardizes TSS limits.

Although problematic, nitrifying wastewater is important for manyreasons. Aside from permit limits, ammonia (NH₃) is toxic to fish andother aquatic life. Ammonia (NH₃) discharges also place a very highoxygen demand on the receiving streams. Nitrification also aids inproducing a highly stabilized effluent.

When all of the ammonia (NH₃) is converted to nitrate (NO₃ ⁻ ), it isremoved from the system or denitrified. Denitrification requires ananoxic zone within the wastewater treatment facility. Regardless ofwhere and how it is done, the principles of operating an anoxic zone arealways the same. First, dissolved oxygen levels must be as low aspossible without reaching 0.0 mg/L. A safe target point to avoidsepticity while starting an anoxic zone is 0.5 mg/L. A good operatingpoint is 0.2 mg/L.

Second, a carbon source must exist for denitrification to occur. A“carbon source” supplies life energy to the bacteria. A carbon sourcecompound may include additional elements to carbon, such as hydrogen andoxygen. The bacteria also must have oxygen to be able to utilize thecarbon. They obtain oxygen from the easiest sources in the order of: (1)free and dissolved oxygen; (2) nitrate (NO₃ ⁻ ); and then (3) sulfate(SO₄ ⁻⁻ ). If the environment has no free or dissolved oxygen, thebacteria obtain oxygen by breaking down nitrate (NO₃ ⁻ ) returned to theanoxic zone in the form of activated sludge. As the bacteria use thenitrate (NO₃ ⁻ ) as an oxygen source to break down the carbon, theirfood source, nitrogen gas is released to the atmosphere as follows:

bacteria+Carbon Source+Nitrate(NO₃ ⁻ )=Nitrogen Gas(N₂)+CarbonDioxide(CO₂)+3.6 parts Alkalinity+Water(H₂O)

When all of the nitrate (NO₃ ⁻ ) is used up, the bacteria look foroxygen from available sulfate (SO₄ ⁻ ). As the sulfates are used up, thefree sulfides will combine with hydrogen to form hydrogen sulfide, whichhas a characteristic “rotten egg” odor. Thus, treatment plant operatorsare can always tell when all of the nitrate (NO₃ ⁻ ) is being convertedinto nitrogen gas (N₂).

Raw influent can be used as a carbon source. However, most treatmentplants supplement the carbon source, for example, by injecting methanol,ethanol or other like carbon sources. Roughly 2.0-2.5 parts methanol isrequired for every part nitrate (NO₃ ⁻ ) that is denitrified.

The mixed liquor suspended solids concentration must be kept in balancewith the carbon source supply. In other words, the carbonsource-to-microorganisms ratio should be in the proper range, on thelower end, for the type of process operating. The pH of the anoxic zoneshould be close to neutral (7.0) and never drop below 6.5.

Optimal denitrification occurs when as much as possible of the nitrate(NO₃ ⁻ ) is converted into nitrogen gas (N₂). Achieving this requires asufficient amount of a carbon source so that the indigenousheterotrophic bacteria will consume all of the dissolved oxygen as wellas the oxygen from the nitrate (NO₃ ⁻ ), thereby converting as much aspossible of the nitrate (NO₃ ⁻ ) into nitrogen gas (N₂).

Many carbon sources for denitrification have been studied and utilizedin wastewater treatment systems. The most popular include the simplealcohols methanol [15] and ethanol [3]. Acetate in the form of eitheracetic acid [1] or some acetate salt, e.g. sodium acetate [7], has alsobeen used. “Acetate” refers to either the ion, as in sodium acetate, orthe substituent group, as in ethyl acetate [6]. The studies frequentlyindicate acetate [7] as the most effective of these listed, and the manyother compounds subjected to these studies.

However, these compounds leave much to be desired for use asdenitrification carbon sources for wastewater treatment units,especially on-site wastewater treatment units. Acetic acid is a solidand corrosive in the pure state. When diluted to safer levels, itbecomes very bulky. Acetate salts also are hazardous solids, and facethe same fate on adequate dilution. Since acetate salts of sodium orpotassium are solids, they must be dissolved for pumping by meteringdevices. These solutions are bulky, and leave solid residue on dryingthat can foul the equipment. The residual from utilization by thebacteria is an increase in alkalinity that is impractical to control inan unattended system.

Among the other compounds used for larger plants are simple alcohols,like ethanol [3] and methanol [15], depicted above, and polyalcoholslike glycerol [2]. These alcohols also have their own limitations withrespect to on-site use.

Fatty acids, monoglycerides, and diglycerides derived from thesaponification of fats also can be used as carbon sources. Short-chainfatty acids are water soluble, while longer-chain fatty acids reducesolubility so that they become surfactants, with soap being the classicexample. Their esters are insoluble.

Fats and oils are esters of glycerin and 3 long chain fatty acids, andare also known as triglycerides [8]. Fatty acids that havecarbon-to-carbon double bonds are referred to as “unsaturated fattyacids” [5].

These traditional supplementary carbon sources, methanol and ethanol,have undesirable characteristics, especially for on-site use, includingacute toxicity; volatile; flammable; and form explosive vapor mixtureswith air in confined spaces. Ethanol, while grain derived in its naturalform is highly regulated and expensive. Cheaper, unregulated denaturedethanol, in excess amounts, inhibits decomposition. It also, whendecomposed, yields byproducts including benzene, ethylene, toluene, andxylene, which should not be released into the environment. Since anexcess of carbon source is needed to ensure that a sufficient amount ofheterotrophic bacteria will locate and convert as much as possible ofthe nitrate (NO₃ ⁻ ) into nitrogen gas (N₂), using denatured ethanolcauses less and less conversion and could build up in the treatment tankand stifles decomposition. Although ethanol is a good carbon source, itmust be converted to acetaldehyde [14], and then acetate before thebacteria can utilize it.

What is needed is a carbon source compound that can deliver theeffectiveness of acetate with none of the above-mentioned issues, andhas only residuals that can be assimilated by the denitrifying bacteria.

One such compound class could be the acetate esters of glycerol. Otherpolyalcohols, such as ethylene glycol [16], propylene glycol [17] andbutylene glycol [19]-[22] also might serve as carriers of acetate in theform of esters, which are combinations of alcohols and organic acids.One example might be 1,2-propylene glycol diacetate [18]. Ethanol andacetic acid combine to form ethyl acetate [6], depicted above.

Many wastewater treatment facilities perform single-tank denitrificationby creating and utilizing anoxic zones. Some examples are:

-   -   (1) Constructing a dedicated anoxic zone at the head of the        aeration tank by installing a baffle and mechanical mixers;    -   (2) Utilizing the first ¼ to ⅓ of the aeration basin as an        anoxic zone by throttling the aeration system diffusers valves        to allow mixing without transferring dissolved oxygen. A        dissolved oxygen probe in the aeration tank tied into a variable        frequency drive that sends a signal to the blowers, providing a        continuous dissolved oxygen level as determined by the set        points; and    -   (3) Utilizing timers to cycle the aeration system on and off        which allows the whole aeration basin to be used intermittently        as an anoxic zone.        These approaches do not completely denitrify the wastewater so        treated.

What are needed, and not taught or suggested in the art, are anapparatus for and method of denitrifying a solution that employs aninexpensive, non-toxic, unregulated carbon source for heterotrophicbacteria to reduce all nitrate (NO₃ ⁻ ) in solution.

SUMMARY OF THE INVENTION

The invention overcomes the disadvantages noted above by providingapparatus for and method of denitrifying a solution that employs aninexpensive, non-toxic, unregulated carbon source that promotes activityof heterotrophic bacteria that reduce all nitrate (NO₃ ⁻ ) in solution.

To that end, an embodiment of an apparatus for denitrifying a solutionconfigured according to principles of the invention includes adenitrification tank configured to receive a portion of the solution fora period of time. Controlling an amount, duration and frequency ofintroduction of polyethylene glycol into the solution promotesindigenous heterotrophic bacteria depleting dissolved oxygen in thesolution and obtaining oxygen from nitrate in the solution.

Another embodiment of an apparatus for denitrifying solution configuredaccording to principles of the invention includes a controller thatreleases an amount of polyethylene glycol into the solution for aduration at a frequency. One or more of the amount, duration andfrequency are determined so that indigenous heterotrophic bacteriadeplete dissolved oxygen in the solution and obtain oxygen from nitratein the solution.

The invention provides improved elements and arrangements thereof, forthe purposes described, which are inexpensive, dependable and effectivein accomplishing intended purposes of the invention.

Other features and advantages of the invention will become apparent fromthe following description of the preferred embodiments, which refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail below with reference to thefollowing figures, throughout which similar reference characters denotecorresponding features consistently, wherein:

FIG. 1 is a vertical, cross-sectional detail view of an apparatusconfigured according to principles of the invention incorporated in awastewater treatment system;

FIG. 2 is a plan view of the embodiment of FIG. 1;

FIG. 3 is a vertical, cross-sectional detail view of an apparatusconfigured according to principles of the invention; and

FIG. 4 is a schematic representation of an embodiment of a methodconfigured according to principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is an apparatus for and method of denitrifying a solutionthat accepts nitrified solution and introduces a carbon source into thesolution that promotes heterotrophic bacterial reduction of nitrate (NO₃⁻ ).

Referring to FIGS. 1 and 2, a denitrification apparatus 100 is shownincorporated in a conventional wastewater treatment plant A. Wastewatertreatment plant A includes a pre-treatment tank B, a treatment tank Cand a holding tank D. Untreated solution flows into the pre-treatmenttank B, into and through the treatment tank C, into and throughdenitrification apparatus 100, into and through the holding tank D, thenis voided into the environment.

Pre-treatment tank B receives raw, untreated wastewater and initiatesthe aerobic phase of treatment during which aerobic bacteria break downthe wastewater. Pre-treatment tank B also retains any non-biodegradablesinadvertently introduced into the system, such as rags and plastic,which settle out prior to introduction of the fluid into the treatmenttank.

Treatment tank C is where the bulk of the aerobic wastewaterdecomposition occurs. Treatment tank C includes walls E and a floor F. Ahopper G mounted in tank C cooperates with walls E and floor F to defineaerator zones H and an interior clarifier chamber I. Diffusers J intreatment tank C promote flow in aerator zones H, which enhances theoxygen content of the wastewater in tank C and aerobic breakdown ofsolid matter therein. In aerator zones H, aeration thoroughly mixes theorganic materials of the wastewater with the bacterial population sothat the bacteria attack and reduce the organic materials.

Aerated and reduced wastewater from aeration zones H passes intoclarifier chamber I. The throat-like lower aperture of hopper Gminimizes fluid flow within clarifier chamber and encourages thesettling out of particulate matter in clarifier chamber I back intoaerator zones H for additional breakdown.

Before passing wastewater from clarifier chamber I into holding tank D,the invention provides for denitrification of the wastewater fromclarifier chamber I in denitrification apparatus 100, described ingreater detail below.

Holding tank D receives denitrified wastewater from denitrificationapparatus 100 where it remains for a period of time. Any remainingparticulate matter in the wastewater settles out prior to being pumpedby a pump K out of wastewater treatment system A into the environment.

Referring to FIG. 3, denitrification system 100 preferably includes adenitrification tank 200, a controller 300 and a doser 400.Denitrification tank 200 receives nitrified solution. Controller 300monitors parameters of the solution in denitrification tank 200 andregulates doser 400, which introduces a carbon source intodenitrification tank 200 and cause conditions that are appropriate forcellular respiration and optimal for denitrification, as described ingreater detail below.

Denitrification tank 200 includes an anoxic media cell 205 in whichmedia 210 are suspended. Nitrified solution 215, preferably frompre-treatment tank C, as shown in FIG. 1, from inlet 220 enters the top225 of anoxic media cell 205 and passes through media 210. From media210, the solution passes out of the bottom 230 of anoxic media cell 205.Media-treated solution is displaced by inflow and eventually passes fromdenitrification tank 200 through outlet 235.

Denitrification tank 200, while distinct from or selectably isolatedfrom the rest of a wastewater treatment system, nevertheless may bestructurally integral therewith, attached thereto or disposed therein.

Media 210 encourage growth of denitrifying surface bacteria.

Controller 300 monitors one or more probes 305 in denitrification tank200. Probes 305 measure one or more of the following parameters: pH;dissolved oxygen; influent flow; effluent flow; conductivity;alkalinity; nitrates; and oxidation reduction potential. The dissolvedoxygen level may be ascertained by measuring the levels or amount ofluminescent dissolved oxygen (LDO), nitrites and/or ammonia. Based onone or more parameter values measured for one or more of the parameters,controller 300 causes doser 400 to dispense a carbon source indenitrification tank 200 in an appropriate amount, for an appropriateduration and at appropriate frequencies so that denitrification tank 200exhibits anoxic conditions with sufficient carbon, or otherwise promotesgrowth of denitrifying bacteria and optimal denitrificationcapabilities.

When controller 300 determines that an aerobic condition exists,typically at least 1 g/mL of O₂ controller 300 instructs doser 400 todeliver an amount of a carbon source to denitrification tank 200. Thecarbon source supplies life energy to the bacteria. The bacteria thenobtain oxygen from the easiest sources in the order of: (1) free anddissolved oxygen; (2) nitrate (NO₃ ⁻ ); and then (3) sulfate (SO₄ ⁻⁻ ).This converts the aerobic conditions in denitrification tank 200 toanoxic. Controller 300 also can ensure that denitrification tank 200remains in an anoxic condition for a duration required fordenitrification.

The denitrifying surface bacteria population increases more when exposedto cyclical aerobic-anaerobic conditions, rather than steady-stateaerobic or anaerobic conditions. This is why it is preferable tocultivate the denitrifying surface bacteria population in a distinctdenitrification tank 200 that may be selectably placed, rather thanalways in communication with the wastewater system, and in particular,the aeration tank or aerobic portion thereof. Carefully maintaininganoxic conditions in denitrification tank 200 ensures survival of thebacteria.

If the denitrification tank is aerobic all of the time, aerobes willexist there, and if it is anaerobic all of the time, anaerobes willexist there. Denitrifiers use oxygen for respiration and carbon forfood. If the denitrifiers are already working under anoxic conditions,have food, but lack oxygen, they will use the closest thing availablefor respiration, which is Nitrate, which the denitrifiers convert intowater and N₂ and CO₂.

There also will exist an accumulation of biomass of living and deadbacteria. This biomass most likely uses some of the nitrate for aminoacid and protein formation. Provisions must be made to periodicallyremove and dispose of this biomass. One method might be to return it tothe aeration tank stage.

Utilizing a combination of the alcohols and acetate as a carbon sourceeliminates all of the problems with carbon sources noted above. Acombination that is particularly useful is glycerin and acetate in theform of a mixture of glycerol acetates, known in the bulk productindustry as diacetin. This name derives from that of the most abundantcomponent, 1,3-diacetin [9], but the mixture often contains significantamounts of 1,2-diacetin [10], triacetin [11], glycerol-1-acetate [12],and glycerol-2-acetate [13].

The preferred carbon source is selected from: a diacetin; a glyceroldiacetate; a polyethylene glycol (PEG) and ethers thereof; a glycoldiacetate; and combinations thereof. Diacetin is preferred because it isrich in acetate substituents that have been shown to be exceptionallyeffective in the denitrification process. In addition, it is anon-hazardous material, non-toxic and non-flammable, and does notevaporate or form solids. Diacetin is rich in available carbon. Also,unlike surplus amounts of ethanol and methanol, surplus amounts ofdiacetin do not inhibit the denitrification process.

Acetate is superior to ethanol because ethanol must be convertedbiologically to acetaldehyde [14], and then to acetate before thedenitrifying bacteria can utilize it. Providing a substance that isready for use to the denitrifying bacteria speeds up the denitrificationprocess by eliminating this conversion step.

Diacetin is an excellent carbon source for on-site anoxicdenitrification of solution because it provides a delivery system forthe acetate moiety that meets a number of requirements. What makesglycerol particularly suited for denitrification is that it acts as acarrier for a readily available form of carbon. In layman's terms,glycerol is the carrier, and acetate is the container of the carbon foodsource for the denitrifying bacteria.

Diacetin is acetate attached to glycerin as a backbone. When the acetateis consumed, the bacteria also utilize the remaining glycerin, leavingonly water and carbon dioxide as residuals. The bacteria tolerateinadvertent excesses of diacetin much better than excesses of otherfoods such as ethanol or especially methanol. The intermediateacetaldehyde and formaldehyde produced by these compounds are knownpreservatives (antibacterial).

Diacetin is readily taken up by the facultative bacteria and held foruse until an oxygen source of dissolved oxygen, nitrate, or nitritebecomes available, keeping the food away from the anaerobes. Facultativebacteria are those that can grow with or without oxygen.

Diacetin is a liquid, neutral, non-hazardous, very compact in its carboncontent. It is used as a food additive and in the preparation of tabletsfrom drugs in the powder form. Commercially, it is prepared from thereaction of acetic anhydride and glycerin. Environmental release iseasily handled in small amounts.

While glycerol diacetate seems to be the most useful compound structure,other carbon sources also could be use that derive from fatty acidesters of polyhydroxyl compounds so long as they fulfil the followingconditions:

1. Liquid at all weather temperatures;

2. Readily miscible with water in the proportions of use;

3. Non volatile, nonflammable; and

4. Non toxic.

These requirements eliminate practically all of the class except theglyceryl acetates.

Another class has ether groups as handles that are more likely to betoxic because they are rarely encountered in nature.

Polyhydroxyls have more than one hydroxy (—OH) group on the compound.Ethylene glycol is the simplest member, with two groups (HOCH2CH2OH).Glycerin has three. Simple sugars, like glucose, fructose, etc., havesix.

Diacetin also is know as: Diacetylglycerol; Glycerin Diacetate;Glycerine Diacetate; Glyceryl Diacetate; Glycerol 1,3-diacetate;2-(Acetyloxy)-1-(hydroxymethyl)ethyl acetate.

Ethers of PEG include compounds containing a chain of [—O—CH2CH2-]units, the unit being repeated one or more times, as shown in thegeneral expression of the reaction 14 below. The chain can be capped oneach end by any of large variety of functional groups containing carbon,hydrogen and oxygen. Typically, these compounds are the reactionproducts of ethylene oxide with compounds containing hydroxyl groupsincluding, but not limited to water, alcohols, polyols, and the productsof the reaction that forms PEG and ethers thereof since it will containa hydroxyl group formed in the previous step.

ROH+xEO->RO(PEG)OH  (14)

As shown in reaction 15 below, in each step of the formation of PEG,ethylene oxide (EO) reacts with a hydroxyl, or alcohol group (—OH). Theoxygen in the hydroxyl becomes an ether link, and the oxygen in the EObecomes a new hydroxyl group. This new hydroxyl group then can reactwith another EO to form another link in the PEG chain. These repeatedlinks in the chain give rise to the “poly” name.

The beginning compound can be water or a large or a small alcohol. Ifthe beginning is water, the reaction product will be PEG with twohydroxyl groups, one on each end of the chain.

With any molecule other than water, the product will be an ether of thebeginning molecule and a PEG chain. If the molecule is large, and thechain short, the character of the product molecule will be influenced bythe properties of the starting molecule. In particular, if the startingmolecule is a hydrocarbon based alcohol, as shown in reaction 16 below,which is more fat soluble and insoluble in water, the ether with PEGwill shift it toward being increasingly miscible with water as the PEGchain length increases. This allows the introduction of hydrocarbongroups, which are very effective carbon source for denitrification, intoa water environment.

Preferably, the ethers of PEG employed in the invention are miscible inthe solution being denitrified.

PEG and ethers thereof are useful for denitrifying because the[—O—CH2-CH2-] unit of the PEG chain is biologically convertable byindigenous bacteria into acetic acid, a well established and veryeffective denitrifying carbon source. The compounds may be liquids orsolids which are soluble in water at the desired concentration. They arenot toxic. They do not form explosive mixtures in air. These compoundshave a high concentration of carbon, slightly higher than ethanol. Theyare compatible with a broad range of materials of construction thatmight be used in containers, or in the pumping or metering system.

An exemplary glycol diacetate is ethyleneglycoldiacetate.

Another preferred carbon source is a mixed glycerol ether, as from areaction of an olefin with glycerin. For example, when vegetable oil isreacted with methanol to form biodiesel and a glycerin byproduct, theglycerin then may be reacted with an olefin to form a mixed glycerolether.

Referring again to FIG. 3, doser 400 may include a peristaltic pump 405or other metering mechanism for delivering a predetermined volume of thecarbon source from a container 410 into media cell 205 or influentstream 215. The carbon source provides an energy source for thedenitrifying bacteria, which consumes the available dissolved oxygenfrom the solution in denitrification tank 200, thereby converting theaerobic conditions denitrification tank to anoxic. The denitrifyingbacterial then consume the oxygen in the remaining Nitrate and convertthe nitrate into water, N₂ and CO₂.

Another embodiment of an apparatus for denitrifying solution configuredaccording to principles of the invention includes a sensor or probe 600configured to measure a parameter related to a time of day and/orcircadian rhythm and define a measurement. Probe 600 is operablyconnected to controller 300. Herein, “circadian rhythm” includes typicaldaily flow patterns, such as when inflows tend to be higher or lowerthan average, associated with system 100. One or more probes 600 is/areresponsive to, or responsive to a timer that is responsive to: a clock;a photocell; a photo collector; an infrared sensor; a light-activatedmagnetic film; means for differentiating light and dark; means forascertaining rotation of the earth; and combinations thereof.

Controller 300 monitors probes 600 and compares one or more of theparameter measurements with predetermined values. Based on one or moreparameter values and/or relationships with the predetermined values,controller 300: (1) causes an amount of a carbon source to be introducedinto the solution for a duration and at a frequency; (2) controls inflowto and/or outflow from denitrification tank 200 and/or treatment tank C;or (3) combinations thereof. As with above, one or more of the amount,duration and frequency are determined so that indigenous heterotrophicbacteria deplete dissolved oxygen in the solution and obtain oxygen fromnitrate in the solution.

Optionally, controller 300 controls aeration of the solution. Theaeration may take place in denitrification tank 200 and/or treatmenttank C. The rate of aeration is understood to relate to the rate ofdenitrification, with greater aeration reducing the rate ofdenitrification, as explained above. Therefore, controlling the rate ofaeration of the solution necessarily controls the rate ofdenitrification.

Referring to FIG. 4, a method of denitrifying solution 500 configuredaccording to principles of the invention includes: a step 505 ofmeasuring a parameter of the solution and defining a measurement; a step510 of comparing the measurement with a predetermined value; a step 515introducing into the solution an amount of a carbon source, as describedabove, wherein the frequency and duration of the introducing and/or theamount is determined according to a relationship between the measurementand the predetermined value.

Step 505 may involve measuring one or more of: pH; dissolved oxygen;influent flow; effluent flow; conductivity; alkalinity; nitrates; andoxidation reduction potential.

Step 510 may involve establishing data in a memory of the controlleragainst which the controller may compare the measurement of step 505.Simple or elaborate conditions or logic statements may be defined fordetermining when an appropriate aerobic condition exists, followingwhich anoxic conditions may be appropriate.

Step 515 may involve instructing a doser to deliver an amount of acarbon source to the denitrification tank. Step 515 is timed and cycledso as to cause conditions in the solution to be anoxic, which promotesthe growth of indigenous denitrifying bacteria. The amount of the carbonsource also may be tailored to create conditions desired for optimaldenitrification. The amount should be sufficient and within a shortenough duration to remove the dissolved oxygen from the solutionsufficiently so that the indigenous bacteria are forced to draw oxygenfrom the remaining nitrate.

The invention is not limited to the particular embodiments described anddepicted herein, rather only to the following claims.

1. Apparatus for denitrifying a solution comprising a denitrificationtank configured to receive a portion of the solution for a period oftime wherein controlling an amount, duration and frequency ofintroduction of a carbon source into the solution promotes indigenousheterotrophic bacteria depleting dissolved oxygen in the solution andobtaining oxygen from nitrate in the solution; wherein said carbonsource is selected from: polyethers of monoglycerides; polyethers of anddiglycerides; and combinations thereof.
 2. Apparatus for denitrifying asolution comprising a denitrification tank configured to receive aportion of the solution for a period of time wherein controlling anamount, duration and frequency of introduction of a carbon source intothe solution promotes indigenous heterotrophic bacteria depletingdissolved oxygen in the solution and obtaining oxygen from nitrate inthe solution; wherein said carbon source is selected from: ethoxylatedmonoglycerides; propoxylated monoglycerides; ethoxylated diglycerides;propoxylated diglycerides; and combinations thereof.
 3. Apparatus fordenitrifying a solution comprising a denitrification tank configured toreceive a portion of the solution for a period of time whereincontrolling an amount, duration and frequency of introduction of acarbon source into the solution promotes indigenous heterotrophicbacteria depleting dissolved oxygen in the solution and obtaining oxygenfrom nitrate in the solution; wherein said carbon source is acarboxcylic acid ester of a diol.
 4. Apparatus of claim 3, wherein saidcarbon source is selected from: ethylene glycol diacetate; propanedioldiacetate; propanediol acetate; diethyleneglycol diacetate;diethyleneglycol acetate; ethylene glycol diformate; propanedioldiformate; propanediol formate; diethyleneglycol diformate;diethyleneglycol formate; ethylene glycol dipropionate; propanedioldipropionate; propanediol propionate; diethyleneglycol dipropionate;diethyleneglycol propionate; ethylene glycol dibutyrate; propanedioldibutyrate; propanediol butyrate; diethyleneglycol dibutyrate;diethyleneglycol butyrate; butylglycol acetate; butyldiglycol acetate;2-ethylhexyl acetate; isopropylglycol acetate; triethyleneglycoldiacetate; and combinations thereof.
 5. Apparatus for denitrifying asolution comprising a denitrification tank configured to receive aportion of the solution for a period of time wherein controlling anamount, duration and frequency of introduction of a carbon source intothe solution promotes indigenous heterotrophic bacteria depletingdissolved oxygen in the solution and obtaining oxygen from nitrate inthe solution; wherein said carbon source is a polyether.
 6. Apparatus ofclaim 5, wherein said carbon source is selected from: polypropyleneglycol; polybutylene glycol; block polymers of ethylene oxide andpropylene oxide; and combinations thereof.
 7. Apparatus for denitrifyinga solution comprising a denitrification tank configured to receive aportion of the solution for a period of time wherein controlling anamount, duration and frequency of introduction of a carbon source intothe solution promotes indigenous heterotrophic bacteria depletingdissolved oxygen in the solution and obtaining oxygen from nitrate inthe solution; wherein said carbon source is a glycoside ester. 8.Apparatus of claim 7, wherein said carbon source is selected from:acetate esters of glucose; lauroyl glucose ester; and combinationsthereof.
 9. Apparatus for denitrifying a solution comprising adenitrification tank configured to receive a portion of the solution fora period of time wherein controlling an amount, duration and frequencyof introduction of a carbon source into the solution promotes indigenousheterotrophic bacteria depleting dissolved oxygen in the solution andobtaining oxygen from nitrate in the solution; wherein said carbonsource is an alkylether of a polyol.
 10. Apparatus of claim 9, whereinsaid carbon source is selected from: ethyl glycerol ether; diethylglycerol ether; ethoxy ethyl glycerol ether; butyl ethyleneglycol ether;isopropyl glycerol ether; polypropylene glycol glycerol ether; lauryldiglucoside; and combinations thereof.
 11. Apparatus for denitrifying asolution comprising a denitrification tank configured to receive aportion of the solution for a period of time wherein controlling anamount, duration and frequency of introduction of a carbon source intothe solution promotes indigenous heterotrophic bacteria depletingdissolved oxygen in the solution and obtaining oxygen from nitrate inthe solution; wherein said carbon source is a carboxcylic acid ester ofan ether of glycerol.
 12. Apparatus of claim 11, wherein said carbonsource is selected from: ethyl ethyl glycerol ether diacetate;dipropylglycerol ether butyrate; and combinations thereof.
 13. Apparatusfor denitrifying a solution comprising a denitrification tank configuredto receive a portion of the solution for a period of time whereincontrolling an amount, duration and frequency of introduction of acarbon source into the solution promotes indigenous heterotrophicbacteria depleting dissolved oxygen in the solution and obtaining oxygenfrom nitrate in the solution; wherein said carbon source is apolysorbate.
 14. Apparatus of claim 13, wherein said carbon source isselected from: polyoxyethylene sorbitan monolaurate; polyoxyethylenesorbitan monooleate; polyoxyethylene sorbitan monostearate;polyoxyethylene sorbitan monopalmitate; and combinations thereof. 15.Apparatus for denitrifying a solution comprising a denitrification tankconfigured to receive a portion of the solution for a period of timewherein controlling an amount, duration and frequency of introduction ofa carbon source into the solution promotes indigenous heterotrophicbacteria depleting dissolved oxygen in the solution and obtaining oxygenfrom nitrate in the solution; wherein said carbon source is selectedfrom: a mixed ether of a polyol; a mixed ester of a polyol; andcombinations thereof.
 16. Apparatus of claim 15, wherein said carbonsource is selected from: ethoxyglycerol ether acetate;1-(2-ethylhexyl)glycerol ether; polypropoxyglycerol ether diacetate;ethoxy glycerol ether diacetate; and combinations thereof.
 17. Apparatusfor denitrifying a solution comprising a denitrification tank configuredto receive a portion of the solution for a period of time whereincontrolling an amount, duration and frequency of introduction of acarbon source into the solution promotes indigenous heterotrophicbacteria depleting dissolved oxygen in the solution and obtaining oxygenfrom nitrate in the solution; wherein said carbon source is a polyol.18. Apparatus of claim 17, wherein said carbon source is selected from:1,2,6-hexanetriol; 1,2,4-butanetriol; pentanetriol; and combinationsthereof.
 19. Apparatus for denitrifying a solution comprising adenitrification tank configured to receive a portion of the solution fora period of time wherein controlling an amount, duration and frequencyof introduction of a carbon source into the solution promotes indigenousheterotrophic bacteria depleting dissolved oxygen in the solution andobtaining oxygen from nitrate in the solution; wherein said carbonsource is an ether of glycerol.
 20. Apparatus of claim 19, wherein saidcarbon source is a mixed glycerol ether.
 21. Apparatus for denitrifyinga solution comprising a denitrification tank configured to receive aportion of the solution for a period of time wherein controlling anamount, duration and frequency of introduction of a carbon source intothe solution promotes indigenous heterotrophic bacteria depletingdissolved oxygen in the solution and obtaining oxygen from nitrate inthe solution; wherein said carbon source is a sorbitan.
 22. Apparatus ofclaim 21, wherein said carbon source is selected from: sorbitanmonolaurate; sorbitan monooleate; sorbitan monotristearate; sorbitanmonopalmitate; and combinations thereof.
 23. Apparatus for denitrifyinga solution comprising a denitrification tank configured to receive aportion of the solution for a period of time wherein controlling anamount, duration and frequency of introduction of a carbon source intothe solution promotes indigenous heterotrophic bacteria depletingdissolved oxygen in the solution and obtaining oxygen from nitrate inthe solution; wherein said carbon source is a polyethyleneglycol ester.24. Apparatus of claim 23, wherein said carbon source is selected from:polyethyleneglycol monolaurate; polyethyleneglycol monooleate;polyethyleneglycol dioleate; polyethyleneglycol monostearate;polyethyleneglycol distearate; polyethyleneglycol monostearate;polyethyleneglycol diricinoleate; and combinations thereof. 25.Apparatus for denitrifying a solution comprising a denitrification tankconfigured to receive a portion of the solution for a period of timewherein controlling an amount, duration and frequency of introduction ofa carbon source into the solution promotes indigenous heterotrophicbacteria depleting dissolved oxygen in the solution and obtaining oxygenfrom nitrate in the solution; wherein said carbon source is selectedfrom: polyglycerol; esters of polyglycerol; and combinations thereof.26. Apparatus of claim 25, wherein said carbon source is selected from:diglycerol; triglycerol; diglycerol caprate, triglycerololeate;diglycerololeate; diglycerolstearate; triglycerolstearate; andcombinations thereof.